title: Thermodynamic and kinetic study of cleavage of the N-O bond of N-oxides by a vanadium(III) complex: enhanced oxygen atom transfer reaction rates for adducts of nitrous oxide and mesityl nitrile oxide.
abstract: Thermodynamic, kinetic, and computational studies are reported for oxygen atom transfer (OAT) to the complex V(N[t-Bu]Ar)3 (Ar = 3,5-C6H3Me2, 1) from compounds containing N-O bonds with a range of BDEs spanning nearly 100 kcal mol(-1): PhNO (108) > SIPr/MesCNO (75) > PyO (63) > IPr/N2O (62) > MesCNO (53) > N2O (40) > dbabhNO (10) (Mes = mesityl; SIPr = 1,3-bis(diisopropyl)phenylimidazolin-2-ylidene; Py = pyridine; IPr = 1,3-bis(diisopropyl)phenylimidazol-2-ylidene; dbabh = 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene). Stopped flow kinetic studies of the OAT reactions show a range of kinetic behavior influenced by both the mode and strength of coordination of the O donor and its ease of atom transfer. Four categories of kinetic behavior are observed depending upon the magnitudes of the rate constants involved: (I) dinuclear OAT following an overall third order rate law (N2O); (II) formation of stable oxidant-bound complexes followed by OAT in a separate step (PyO and PhNO); (III) transient formation and decay of metastable oxidant-bound intermediates on the same time scale as OAT (SIPr/MesCNO and IPr/N2O); (IV) steady-state kinetics in which no detectable intermediates are observed (dbabhNO and MesCNO). Thermochemical studies of OAT to 1 show that the V-O bond in O≡V(N[t-Bu]Ar)3 is strong (BDE = 154 ± 3 kcal mol(-1)) compared with all the N-O bonds cleaved. In contrast, measurement of the N-O bond in dbabhNO show it to be especially weak (BDE = 10 ± 3 kcal mol(-1)) and that dissociation of dbabhNO to anthracene, N2, and a (3)O atom is thermodynamically favorable at room temperature. Comparison of the OAT of adducts of N2O and MesCNO to the bulky complex 1 show a faster rate than in the case of free N2O or MesCNO despite increased steric hindrance of the adducts.
authors.affiliation: Department of Chemistry, Tufts University, 62 Talbot Avenue, Medford, Massachusetts 02155, USA.
authors.forename: Taryn D
authors.initials: TD
authors.lastname: Palluccio
authors.forename: Elena V
authors.initials: EV
authors.lastname: Rybak-Akimova
authors.forename: Subhojit
authors.initials: S
authors.lastname: Majumdar
authors.forename: Xiaochen
authors.initials: X
authors.lastname: Cai
authors.forename: Megan
authors.initials: M
authors.lastname: Chui
authors.forename: Manuel
authors.initials: M
authors.lastname: Temprado
authors.forename: Jared S
authors.initials: JS
authors.lastname: Silvia
authors.forename: Anthony F
authors.initials: AF
authors.lastname: Cozzolino
authors.forename: Daniel
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authors.lastname: Tofan
authors.forename: Alexandra
authors.initials: A
authors.lastname: Velian
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Cummins
authors.forename: Burjor
authors.initials: B
authors.lastname: Captain
authors.forename: Carl D
authors.initials: CD
authors.lastname: Hoff